1. Field of the Invention
The invention is directed to a cylinder in a printing machine, wherein the cylinder is driven by an electric individual drive and is arranged so as to be swivelable with respect to its position by means of a swiveling device, wherein a rotation transducer or rotation sensor is arranged at the cylinder for measuring its angular position with respect to the swiveling device.
2. Description of the Related Art
Recently, there has been an increase in the use of printing machines with individually driven cylinders such, for example, as an offset printing machine with both a form cylinder and a blanket cylinder having an individual electric drive motor. In the offset type of printing machine, the blanket cylinders must be adjusted or moved toward the printing stock web at the start of a printing process and adjusted or moved away from it at the end of the printing process. For this purpose, the blanket cylinders are arranged together with their electric drive arrangement on a swiveling device. The swiveling device is an eccentric element or a rocker type mechanism, for example. The plate cylinder, form cylinder, or other cylinders, such as a printing cylinder, may also be swivelably arranged. When an eccentric element is used, the eccentric element is rotatably mounted in a sidewall of the printing machine. The shaft of the cylinder is eccentrically mounted on the eccentric element with respect to the center of rotation of the eccentric element.
A prior art cylinder for a printing mechanism that is driven by an individual drive, is known from German reference DE 196 24 394 A1. In this prior art cylinder, a hollow neck or journal of the cylinder is received eccentrically on a spindle unit that is mounted, in turn, in a side wall of the printing mechanism. A carrying tube of the spindle unit houses a stator of an electric motor. A rotation sensor housing located on the journal is fastened to the carrying tube for regulating the driving of the motor. For purposes of changing the position of the cylinder relative to an adjacent cylinder, the spindle unit and, accordingly, the carrying tube are rotated. During rotation of the spindle unit, the stator of the motor and the rotation sensor housing are also rotated. Accordingly, the reference angle to which the rotation sensor references the rotational angle position of the journal of the cylinder, and therefore the rotational angle position of the rotor of the motor, is also displaced. This results in an unwanted rotation of the cylinder being moved in relation to the adjacent cylinder cooperating with it.
It has been shown in practice that even small displacement paths between the "print on" and "print off" positions of the cylinder lead to large rotations of the above described eccentric mechanism . For example, displacement paths of 0.1 mm already require 10-degree rotation of the eccentric mechanism. This problem also occurs when a rocker is used as a swiveling device for the cylinder. However, the angular errors occurring with rockers, depending on their length, are smaller than with eccentric mechanisms.
After a swiveling movement is carried out, the intended angular position of the cylinder is displaced not only in relation to the adjacent cylinder, but also in relation to the printing stock web. The movement in relation to the printing stock web occurs because, the blanket cylinder, due to the position regulation, also executes a further movement in addition to its movement corresponding to the web speed of the printing stock when the eccentric mechanism is rotated. The further movement comprises a rotating movement and--corresponding to the offset of the center of rotation of the cylinder from the center of the eccentric--a transverse movement. This movement can cause the printing stock web to tear during the print-on/print-off setting process because the blanket cylinder not only rolls along the surface of the printing stock web, but also causes sliding friction on its surface due to the translational movement. In this respect, the blanket cylinder draws the printing stock web toward it.